1. The Field of Invention
The present invention relates to subcutaneously implanted cannulas used to access the body's circulation. More particularly, this invention provides a cannula and method for establishing intermittent vascular access using an implanted cannula in the general shape of a "T".
The advent of hemodialysis for the treatment of end-stage renal disease has prompted the development of many vascular access devices for the purpose of acquiring and returning large quantities of blood for passage through an extracorporeal circuit during hemodialysis procedure. Available devices have generally relied on the use of either indwelling venous catheters or flow through shunt devices which create an artificial fistula between an artery and vein.
Venous catheters are limited by relatively poor draw flows and by their tendency to be irritative resulting in vessel stenosis, thrombosis, and occasionally vessel perforation. They frequently fail because of infection, weakness in the vessel wall, poor catheter position, and/or thrombus formation in the catheter lumen. Shunt devices which create a fistulous blood flow between an artery and a vein have been the mainstay of modern vascular access for dialysis but are similarly problematic. Installation of these "shunts" is an extensive surgical procedure resulting in significant tissue trauma and pain. Once in place, the shunts result in additional cardiac output needs with as much as one-fifth of the cardiac output (approximately 1000 ml per minute) required for adequate function. In addition, the transfer of the arterial pressure wave results in damage to the vein at the point of anastomosis with the shunt and can result in intimal hyperplasia and subsequent thrombosis and shunt occlusion. When such occlusion occurs, another vein segment must be used for shunt revision, and exhaustion of available sites is distressingly common and can be fatal. Repeated punctures of the wall of the shunt often result in eventual failure and require additional surgery to repair or replace the shunt. The expense in terms of both health care dollars and human misery is enormous.
Each of the available access technologies mentioned thus far are also complicated by the possibility of recirculation of blood already passed through the extra-corporeal circuit resulting in the loss of treatment efficiency. The harm done to patients by the "recirculation syndrome" is insidious and at times undetected until great harm has been done.
Indwelling catheters which occupy only a portion of the vessel lumen are subject to movement within the vessel, which can cause irritation or even vessel perforation. Further, catheters which occupy only a portion of the vessel lumen, and which are inserted or threaded through the lumen for substantial distances tend to disrupt the normal flow of blood through the vascular structure, altering the hemodynamics of the blood flow in a manner which can damage the vessel, the components of the blood, and which can encourage thrombosis. Such catheters are generally unsuitable for long term implantation in arteries.
What is needed is a cannula that can be implanted within an artery and that will cause minimal disruption of blood flow through the lumen of the artery during use and nonuse of the cannula, which does not cause vessel stenosis, thrombosis, or vessel perforation, which is capable of handling large quantities of blood, and which will retain its usefulness for a long period of time after implantation.
2. Description of the Background Art
Vascular access employing indwelling catheters is described in a number of patents and publications including U.S. Pat. Nos. 3,888,249; 4,543,088; 4,634,422; 4,673,394; 4,685,905; 4,692,146; 4,695,273; 4,704,103; 4,705,501; 4,772,270; 4,846,806; 5,053,613; 5,057,084; 5,100,392; 5,167,638; 5,108,365; 5,226,879; 5,263,930; 5,281,199; 5,306,255; 5,318,545; 5,324,518; 5,336,194; 5,350,360; 5,360,407; 5,399,168; 5,417,656; 5,476;451; 5,503,630; 5,520,643; 5,527,277; and 5,527,278; and EP 228 532; and Wigness et al. (1982) paper entitled "Biodirectional Implantable Vascular Access Modality" presented at the Meeting of the American Society for Artificial Internal Organs, Apr. 14-16, 1982, Chicago, Ill.
Catheters having distal valves are described in a number of patents including U.S. Pat. Nos. 274,447; 3,331,371; 3,888,249; 4,549,879; 4,657,536; 4,671,796; 4,701,166; 4,705,501; 4,759,752; 4,846,806; 4,973,319; 5,030,710; 5,112,301; 5,156,600; and 5,224,978.
Implantable dialysis connection parts are described in a number of patents including U.S. Pat. Nos. 4,692,146; 4,892,518; 5,041,098; 5,180,365; and 5,350,360.